AT89C55WD-33AU View Datasheet(PDF) - Atmel Corporation
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AT89C55WD-33AU Datasheet PDF : 35 Pages
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19. Program Memory Lock Bits
The AT89C55WD has three lock bits that can be left unprogrammed (U) or can be programmed
(P) to obtain the additional features listed in the following table.
Table 19-1. Lock Bit Protection Modes
Program Lock Bits
LB1 LB2 LB3 Protection Type
1
U
U
U No program lock features.
MOVC instructions executed from external program memory are
2
P
U
U
disabled from fetching code bytes from internal memory, EA is
sampled and latched on reset, and further programming of the Flash
memory is disabled.
3
P
P
U Same as mode 2, but verify is also disabled.
4
P
P
P Same as mode 3, but external execution is also disabled.
When lock bit 1 is programmed, the logic level at the EA pin is sampled and latched during reset.
If the device is powered up without a reset, the latch initializes to a random value and holds that
value until reset is activated. The latched value of EA must agree with the current logic level at
that pin in order for the device to function properly.
20. Programming the Flash
The AT89C55WD is shipped with the on-chip Flash memory array ready to be programmed. The
programming interface needs a high-voltage (12-volt) program enable signal and is compatible
with conventional third-party Flash or EPROM programmers.
The AT89C55WD code memory array is programmed byte-by-byte.
Programming Algorithm: Before programming the AT89C55WD, the address, data, and con-
trol signals should be set up according to the Flash programming mode table and Figures 21-1
and 21-2. To program the AT89C55WD, take the following steps:
1. Input the desired memory location on the address lines.
2. Input the appropriate data byte on the data lines.
3. Activate the correct combination of control signals.
4. Raise EA/VPP to 12V.
5. Pulse ALE/PROG once to program a byte in the Flash array or the lock bits. The byte-
write cycle is self-timed and typically takes no more than 50 µs. Repeat steps 1
through 5, changing the address and data for the entire array or until the end of the
object file is reached.
20 AT89C55WD
1921D–MICRO–6/08
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